Extract numbers from a filename using std::regex_replace

Question

Extract numbers from a filename using std::regex_replace

Flaviu_ 1,031

I have:

	std::string filename{"my_file01010_asset_103.csv"};
	try
	{
		std::cout << std::regex_replace(filename,
			std::regex("[^0-9+]"), "") << std::endl;
	}
	catch (std::exception& ex)
	{
		std::cerr << ex.what();
	}

How can I extract 103 only?

Minxin Yu 13,501 Reputation points Microsoft External Staff

2024-03-07T01:18:05.8633333+00:00

Just to check, are there any questions left?

1 answer

Your answer

Minxin Yu 13,501 Reputation points Microsoft External Staff

2024-03-07T01:18:05.8633333+00:00

Just to check, are there any questions left?

Answer 1

Viorel 122.5K

For example:

std::string filename{ "my_file01010_asset_103.csv" };
std::regex re( R"((\d+)\.)" );

std::smatch m;
if( std::regex_search( filename, m, re ) )
{
    std::string number = m[1].str( );

    std::cout << number << std::endl;
}

Flaviu_ 1,031

Ok, thanks, but how about using std::regex_replace only?

	std::string filename{"my_file01010_asset_103.csv"};
	try
	{
		std::cout << std::regex_replace(filename,
			std::regex("(\\d+)\\."), "") << std::endl;
	}
	catch (std::exception& ex)
	{
		std::cerr << ex.what();
	}

Ouput this: my_file01010_asset_csv

Viorel 122.5K Reputation points

2024-03-03T19:05:06.7533333+00:00

What is the expected result using regex_replace?

Flaviu_ 1,031

Output should be: 103

I have tried this:

	std::string filename{"my_file01010_asset_103.csv"};
	try
	{
		std::cout << std::regex_replace(filename,
			std::regex(R"((\d+)(?!.*\d))"), "") << std::endl;
	}
	catch (std::exception& ex)
	{
		std::cerr << ex.what();
	}

And I got: my_file01010_asset_.csv, exactly what I need to move out.

Viorel 122.5K Reputation points

2024-03-03T19:28:24.4533333+00:00
Try this:

std::cout << std::regex_replace( filename, std::regex( "(.*?)(\\d+)(\\..+)" ), "$2" ) << std::endl;
Flaviu_ 1,031 Reputation points

2024-03-03T19:50:30.1333333+00:00
It works your solution, can you explain how to correct this one?

std::cout << std::regex_replace(filename, std::regex(R"((\d+)(?!.*\d))"), "") << std::endl;

I mean, why remains everything except last numbers, can you explain?

Thanks.
Viorel 122.5K Reputation points

2024-03-03T20:43:23.8066667+00:00
The pattern (\d+)(?!.*\d) finds the “103”, but this number should be kept.

Try another pattern:

std::cout << std::regex_replace( filename, std::regex( R"(.*?\D(?=\d+\.)|\..*)" ), "" ) << std::endl;

It should find everything except “103”.

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Extract numbers from a filename using std::regex_replace

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